When you mention they refuse to replace the "fuel pump sensor" - I hope you are not referring to the fuel pump relay that sits next to the fuses (under the glove box)?
To change that sucker is step numero uno whenever you have any REX issues.
People have swaped out complete engines to find the relay at fault in the end.
You can change it DIY and the part is approx. 15.- Euro!
https://nemigaparts.com/cat_spares/etk/ ... 1/61_3564/